Sterilization of textile materials is typically conducted by consumers and service providers (e.g., hospitals, nursing homes and hotels) using a conventional aqueous immersive laundry process or dry cleaning methods. Conventional laundering requires relatively large amounts of water, and the articles are subject to fading and deterioration after repeated washes. Dry cleaning processes rely on non-aqueous solutions for cleaning. However, the large amounts of solvents and the need for dedicated dry cleaning operations make this form of cleaning inconvenient and expensive. Additionally, while the conventional and dry cleaning processes may be effective to remove body soils, dirt and/or stains, they do not effectively sterilize the fabric articles or textiles, posing a public health problem in hotels, inns, and particularly in hospitals, clinics and nursing homes, where visitors and indwellers are less immune to infectious microbes.
Recent advances in textile technology have produced textiles having microbiocidal agents incorporated in or on the surface of the fabric article or textile. For example, metal based inorganic compounds such as silver (Ag), zinc oxide (ZnO) or titanium dioxide (TiO2) can be utilized as microbiocidal agents and have been adapted for incorporation on or in a variety of different substrates and surfaces. Such inorganic compounds have been incorporated within melt spun synthetic fibers in order to provide fabric articles which antimicrobial characteristics. This method incorporates these antimicrobial compounds into the bulk of the melt-spun fibres. As microbial attack initiates and continues mostly on the surface and the subsurface region of textiles, bulk incorporation of antimicrobial compounds by using e.g. melt spinning is a inefficient method as it rarely keeps the antimicrobial agent at the surface.
A contact with solid surfaces provides microbes a favorable environment to grow and spread. A method that kills microbes on contact will make effective microbiocidial surface. Attempts have been made to apply such metal-based microbiocidal agents on the surfaces of fabrics, with little success from a durability standpoint. For example, spray methods and dip-coating techniques have been utilized to apply inorganic compounds to fibers prior to or after weaving or knitting. However, such techniques are not wash-durable, resulting not only in a loss of antimicrobial properties after a few washes, but also an increase in environmental pollution due to the elution of loose microbiocidal agents into the effluent. Moreover, the poor adhesion characteristics of such metal-based compounds to fabric articles or other textiles can pose a serious health risk to individuals wearing or in direct contact with such articles.
The major difficulty in surface incorporation of microbiocidal agents into textiles lies in the adhesion and binding of these agents to the surface of the textiles. Textile fibres are made of either natural or synthetic polymers or a blend of these two.
It is known in the art that some of the natural and synthetic polymers used in textiles are thermoplastic in nature i.e. they deform when heated.
While techniques have been used to improve the adhesion of these inorganic compounds to the surface of textiles, e.g. by chemical functionalization of the textile surface with organic molecules, or by modification of a polymer surface by physical means (e.g., low temperature, high pressure plasma treatments) they still suffer from poor durability due to the problem associated with binding of inorganic microbiocidal agents to textile surfaces. Such techniques are therefore unsuitable in industrial textile applications due to the level of expense and environmental pollution.
A number of metal-based microbiocidal agents owes there anti-microbial actions due to surface interactions with microbes either directly through penetration or indirectly through the generation of antimicrobial species such as nascent oxygen, hydroxyl or peroxy ion produced as a result of photocatalytic activity.
In many cases, these metal based microbiocidal agents are nanoparticles i.e. at least one dimension of these nanoparticles (height, width or length) is smaller than 100 nm (10−7 m).
It is known in the art that such a smaller dimension enormously increases the surface area in nanoparticles. Nanoparticles are also known to possess extraordinary and otherwise impossible crystal structures, morphology and physic-chemical properties such as photocatalytic properties, photoluminescence, high yield point, superior electronic conduction, superhydrophobicity etc. Nanoparticles, due to their enormous surface area, may also possess very high surface energy and activity, which often forces them to form clusters or aggregates. While the effective surface area reduces if nanoparticles aggregates or clusters, it can be still much higher than that available e.g. from their micro-size counterparts.
It is usually the frontal surface of a textile product exposed to the ambient environment that is more prone to the growth and spread of microbes. Paradoxically, this frontal surface is also exposed to photons from sunlight or any suitable artificial light source, which can more effectively cleanse the textile surface through photocatalytic actions, for example. The microbiocidal actions take place at the surfaces of these metal based microbiocidal agents, which means that a higher amount of surface area exposed to the ambient will result in a larger extent of surface reactions to kill microbes.
Currently, most techniques to produce inorganic compound-based antimicrobial finishes or surface coatings on textiles yield a relatively thick, often continuous, two-sided coating on the textile product. A continuous coating of microbiocidal agents on textiles is unnecessary due to the colloidal nature and finite size of microbes during their planktonic stage of growth during which the action of microbiocidal action is most effective. It also has the limitation of resulting in a weaker interface due to the inherent difficulty in achieving a strong bonding with the textile surface over a large area. A thick coating accentuates this problem by further weakening the interface due to the mismatch of elastic properties between harder metal-based microbiocidal agents and the soft and compliant textiles matrix. This increases the risk of dislodgement of microbiocides during use and cleaning operations. It also significantly reduces the surface area of the microbiocide that would have been otherwise available to kill bacteria.
Application of microbiocidal agents on both sides of a textile product is also less meaningful if the microbiocidal action takes place on the surface that is exposed to the stimulus (e.g. a photon from a light source) that is responsible for the microbiocidal action.